In many technical applications flexible belts or ‘strips’ are used. Such strips generally are made from elongated strength members, which will be called ‘cords’ hereinafter, arranged parallel to one another in the plane of the strip. In many cases the strips are encased in a polymer material or ‘matrix’ although other binding methods such as weaving or knitting are also possible to hold the cords together. The strips have a substantially oblong cross section. The anisotropic nature of such strips, being flexible in a direction perpendicular to the plane of the cords and rigid in that plane while being strong mainly in the lengthwise direction, makes them particularly suited to take up tension in static or dynamic applications.
In dynamic applications strips can be found as conveyor belts (to transfer materials), transmission belts (to transfer power) with a flat or with a teethed surface for optimum grip (the latter are known as synchronous or timing belts), elevator belts (to carry the cart of an elevator) or also as rubber tracks (for moving vehicles on difficult terrain). In static applications strips can be used to reinforce for example pipes wherein an internal tubular member is reinforced by helically wound strips around it (as described in FR 2914040 or WO 2002/090812).
Whenever a long length of strip is required it will be necessary to connect different shorter lengths of strip into a single long length. Such a connection is called a ‘splice’ or a ‘joint’. Indeed, there is a maximum to the possible length of strip that can be uninterruptedly produced. For example for a conveyor belt, the length of a single stretch is limited by the magnitude and weight of the roll of belt that has to remain transportable to the installation site. Different stretches of belts are connected one to another on site. Finally the belt is closed by splicing the final closure over the driving drums and idlers. A good overview of different splicing families that are used in the field of conveyor belts can be found in “Design of Steel Cord Conveyor Belt Splices” by M. Hager and H. von der Wroge in “Belt Conveyor Technology, I/94” out of “The Best of Bulk Solids Handling 1986-1991” published by Trans Tech Publications.
Another need for strip splicing occurs when one wants to close a strip into a single loop i.e. to make it endless. This is for example the case for timing belts that are made in long lengths and afterwards cut to length and spliced. See e.g. U.S. Pat. No. 3,419,449.
An ideal splice should not be noticeable in the strip. The splice must therefore have:    (A). Equal breaking strength as the strip;    (B). Equal stiffness in stretching as well as in bending as the strip itself;    (C). Equal dimensions as the strip (no thicker sections)    (D). Show equal dynamic fatigue as the strip;    (E). Should be relatively easy to implement on site.
In principle an ideal splice could be made when the length of the splice is unlimited. However, this is not practical.
Hence, making practical splices is always compromising between the different requirements (A) to (E) mentioned above. One type of splice may therefore be perfectly fit in one application, but not for connecting another kind of strips in another application. The following splice methods are known:                Splice by means of mechanical fasteners: a row of clamps are attached to the edge of the belt that is cut perpendicular to its length. A connecting rod is introduced into the inter-digitised eyelets formed. This kind of splice is used for fabric reinforced types of strips. It can not be used for strips with mainly axial reinforcement (the clamps tear out). As the splice is like a hinge, it is more flexible than the strip itself.        Overlap splice: the ends of the strips are overlapped and are vulcanized or glued to one another. This kind of splice is sometimes used to make rubber tracks endless. It has an increased bending stiffness in the splicing area because the two cord planes of both ends do not coincide and form a stiff double layer.        Interlocking splice: the ends of the strips are cut in the plane of the strip according a pattern with protrusions and recesses that fit into one another (like a dovetail connection). Afterwards the splice is vulcanized or glued or molten together. See for example WO 2009/040628.        
The following splices are described in ISO 15236-4.                Finger splices are splices in which the ends of the strips are cut into a mating saw tooth pattern. The ‘fingers’ are afterwards vulcanized to one another. It is mainly used for fabric reinforced belts or strips.        Interlaced stepped splices. Cord ends from one strip are arranged—‘interlaced’—between cords of the other strip end and subsequently covered with rubber or polymer or glued together. The ends of the cords usually finish at regular positions in the splice hence its name of ‘stepped splice’. In an ‘interlaced stepped splice’, the number of cords in the splice area is always larger than then number of cords in the strip. Interlaced stepped splices can only be used if the strip has less than about 50% packing degree. With packing degree is meant the ratio of the sum of all cord diameters to the total width of the strip. In case of a larger packing degree, some cords will have to be cut at the splice entry from both belts in order to accommodate space for the inserted cords. Although such a splice has a very good static strength (the splice can be stronger than the belt), it shows an increased stiffness in the splice area since more cords are present than in the strip itself.        Plain stepped splices. The number of cords within the splice remains equal to the number of cords in the strip. In other words: the cord ends of both strips abut to one another. Different lay-out patterns are possible such as an ‘organ pipe splice’ (having a repeating 01230123 . . . pattern, the numbers indicating the step length of the cord ends of one strip in the splice) or a ‘fir tree splice’ (having a repeating 01232100123210 . . . ) pattern. Such splices are difficult to discern from the strip itself in terms of bending stiffness, axial stiffness and section. However, they show a lower strength compared to ‘Interlaced stepped splices’.        
The inventors were primarily concerned with finding a splice that showed uniform bending properties over the splice. In second order—but still very important—there was the need to retain as much as possible strip strength through the splice. As the strip concerned has a rather high packing density (more than 50%) there was no other possibility than to opt for a “plain stepped splice”. Although such type of splices are known for quite a long time (see e.g. U.S. Pat. No. 1,735,686 of 1926 and U.S. Pat. No. 3,101,290 of 1963) they found other and better ways of defining patterns and lay-outs that are the subject of this patent application.